The ancient Greeks

The Greek philosophers from as early as Pythagoras (c. 582 BC-c. 497 BC) believed that light came from 'visible' things and that our eyes received the tiny particles of light. The philosopher and statesman Empedocles (5th century BC), originator of the idea of four elements — earth, air, fire and water (and two moving forces, love and strife) — also made a number of assertions about light. He believed that light came from luminous objects but that light rays also came out from the eyes. In addition, he proposed that light travels at a finite speed.

The Greek mathematician Euclid (c. 325 BC-c. 265 BC), perhaps better known for his works on geometry, is also believed to have thought that the eyes send out rays of light and that this gives the sensation of vision. Euclid studied mirrors, and the law of reflection is stated in a book entitled Catoptrics, thought to have been written by him in the 3rd century BC.